Re: [RFC] tty/sysrq: Add alternative SysRq key

[Randy Dunlap]

On 11/3/21 8:54 AM, Andrzej Pietrasiewicz wrote:
> There exist machines which don't have SysRq key at all, e.g. chromebooks.
>
> This patch allows configuring an alternative key to act as SysRq. Devices
> which declare KEY_SYSRQ in their 'keybit' bitmap continue using KEY_SYSRQ,
> but other devices use the alternative SysRq key instead, by default F10.
> Which key is actually used can be modified with sysrq's module parameter.
>
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>
> ---
> I'd like to resurrect an old thread regarding supporting alternative SysRq
> key for machines which don't have a physical SysRq key at all.
>
> The old thread:
>
> https://www.spinics.net/lists/linux-input/msg67982.html
>
> I'm resending this patch, rebased onto v5.15.
>
> Any (new) thoughts about it?

Hi,
Did you test it with this patch?


>   drivers/tty/sysrq.c | 28 +++++++++++++++++++++++++---
>   1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index c911196ac893..6dd288e53ce9 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -634,6 +634,7 @@ EXPORT_SYMBOL(handle_sysrq);
>   
>   #ifdef CONFIG_INPUT
>   static int sysrq_reset_downtime_ms;
> +static unsigned short alternative_sysrq_key = KEY_F10;
>   
>   /* Simple translation table for the SysRq keys */
>   static const unsigned char sysrq_xlate[KEY_CNT] =
> @@ -653,6 +654,7 @@ struct sysrq_state {
>   	unsigned int alt_use;
>   	unsigned int shift;
>   	unsigned int shift_use;
> +	unsigned short sys

That line appears to need an ending ';'.
Or maybe that line was truncated since 'sys' isn't used anywhere in this patch.

>   	bool active;
>   	bool need_reinject;
>   	bool reinjecting;
> @@ -802,10 +804,10 @@ static void sysrq_reinject_alt_sysrq(struct work_struct *work)
>   
>   		/* Simulate press and release of Alt + SysRq */
>   		input_inject_event(handle, EV_KEY, alt_code, 1);
> -		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
> +		input_inject_event(handle, EV_KEY, sysrq->sysrq_key, 1);
>   		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
>   
> -		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
> +		input_inject_event(handle, EV_KEY, sysrq->sysrq_key, 0);
>   		input_inject_event(handle, EV_KEY, alt_code, 0);
>   		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
>   
> @@ -845,6 +847,7 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
>   			sysrq->shift = code;
>   		break;
>   
> +key_sysrq:
>   	case KEY_SYSRQ:
>   		if (value == 1 && sysrq->alt != KEY_RESERVED) {
>   			sysrq->active = true;
> @@ -867,11 +870,15 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
>   		 * triggering print screen function.
>   		 */
>   		if (sysrq->active)
> -			clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
> +			clear_bit(sysrq->sysrq_key, sysrq->handle.dev->key);
>   
>   		break;
>   
>   	default:
> +		/* handle non-default sysrq key */
> +		if (code == sysrq->sysrq_key)
> +			goto key_sysrq;
> +
>   		if (sysrq->active && value && value != 2) {
>   			unsigned char c = sysrq_xlate[code];
>   
> @@ -970,6 +977,14 @@ static int sysrq_connect(struct input_handler *handler,
>   	sysrq->handle.private = sysrq;
>   	timer_setup(&sysrq->keyreset_timer, sysrq_do_reset, 0);
>   
> +	if (test_bit(KEY_SYSRQ, dev->keybit)) {
> +		sysrq->sysrq_key = KEY_SYSRQ;
> +		pr_info("%s: using default sysrq key [%x]\n", dev->name, KEY_SYSRQ);
> +	} else {
> +		sysrq->sysrq_key = alternative_sysrq_key;
> +		pr_info("%s: Using alternative sysrq key: [%x]\n", dev->name, sysrq->sysrq_key);
> +	}
> +
>   	error = input_register_handle(&sysrq->handle);
>   	if (error) {
>   		pr_err("Failed to register input sysrq handler, error %d\n",
> @@ -1078,6 +1093,13 @@ module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
>   
>   module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
>   
> +module_param(alternative_sysrq_key, ushort, 0644);
> +MODULE_PARM_DESC(alternative_sysrq_key,
> +	"Alternative SysRq key for input devices that don't have SysRq key. F10 by default.\n"
> +	"Example\n"
> +	"Using F9 as SysRq:\n"
> +	"sysrq.alternative_sysrq_key=0x43\n");
> +
>   #else
>   
>   static inline void sysrq_register_handler(void)


--
~Randy